Shares in Australia outperformed their global peers throughout the 2000s, as the global commodities ''supercycle'' ramped up, thanks to the industrialisation of economies across Asia and the developing world.

But recently, our market has shed its reputation for producing better returns than the rest of the world. In the past six months, for instance, the benchmark ASX 200 index is close to flat, compared with a rise of 7 per cent on Wall Street.

This may seem surprising, because although the economy has weakened, it's still a lot healthier than that of the US.

So why are Australian shares losing their allure compared with those in the US? And what are the implications for investors?

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The main reason for the slump is our oversized resources sector. Mining and energy stocks make up about a quarter of the benchmark ASX 200 index - a far bigger share than in most developed countries. This means the sharemarket is heavily influenced by the health of the resources sector - which in turn is affected greatly by what's happening overseas.

Since the US Federal Reserve chairman Ben Bernanke signalled his intent to start winding back stimulus in May, global investors have been yanking their capital from developing or ''emerging'' countries - which happen to be the main source of growth for our mining companies.

As the graph shows, the poor performance of mining stocks has acted as a weight on the rest of the market all year. In fact, if it wasn't for the bumper performance of financial stocks, the entire market would have struggled in the past few months.

Investors' retreat from the emerging world could just be a passing fad, of course. Markets are notoriously fickle - there's a chance investors will pour money back into developing economies' financial markets when conditions improve.

More and more, however, it looks like a long-term shift.

A growing number of analysts are arguing that the rapidly-expanding BRIC (Brazil, Russia, India and China) economies are reaching the end of a phase in their growth spurt.

If this is correct, and these growth engines are in for a weak patch, it suggests things could remain soft for Australia's mining industry.

With mining playing such a big part in the local index, and when Australia's biggest trading partners are in Asia, weakness in the emerging world is likely to affect us more than other wealthy nations.